The Congress is about to assert its constitutional role over war powers. Last December, the Senate voted to end US assistance for the Saudi-led coalition’s participation in the civil war in Yemen. The US has been providing logistical and intelligence support, including aerial refueling (now ceased), for the Saudi’s military action against the Iranian-backed rebels in Yemen. The war has caused widespread civilian casualties and starvation conditions in Yemen, and Saudi Arabia has been widely condemned for its method of warfare. For their part, Saudi Arabia claims Iran is spreading its influence to the southern border of Saudi Arabia, and has been no less cruel in its manner of warfare.

The view of the Senate last December was that America had no vital interest in participating in this war, and that Saudi Arabia’s conduct of the war was unconscionable. The vote happened at the height of outrage over the Saudi killing of Washington Post columnist Khashoggi in Turkey and signaled that America needed to dissociate itself from Saudi Arabia. Seven Republican Senators joined all the Senate Democrats in voting for the resolution; three other Senate Republicans did not vote.

The new House of Representatives has just voted for a similar resolution. Under the 1973 War Powers Resolution (“WPR,” passed over President Nixon’s veto in 1973), the Senate is now obliged to take up the House resolution (after a short procedural delay). It will in all likelihood pass the Senate again, and then go to President Trump who will veto it. Neither house of Congress approved with more than 2/3 vote, so the veto will likely not be overridden.

That, however, is not the end of this matter. If the US involvement in Yemen constitutes war (or even just “hostilities,” according to the WPR) advance approval by Congress was legally required. The veto of the disapproval resolution doesn’t change that. Members of Congress will bring a lawsuit to compel President Trump to withdraw all US military from hostilities in Yemen.

In 1999, I, and thirty other Members of Congress, sued President Clinton for waging war in then-Yugoslavia, without the approval of Congress. Our lawsuit was not permitted to proceed, despite the fact that the United States was undoubtedly engaged in hostilities there (with daily bombing raids over Belgrade). The lower federal courts ruled that Congress had not spoken unequivocally, since the House had defeated a formal declaration of war but also refused to approve a resolution calling for the US to cease hostilities. Further, the lower federal courts ruled Members of Congress were not specifically hurt, while suggesting a member of the military might have sufficient legal standing to bring the suit instead.

Both these flaws have been corrected in the Yemen situation. Congress will have spoken authoritatively, and the Members of Congress advancing this challenge will likely find a member of the armed services involved in some aspect of the hostilities in Yemen willing to join the lawsuit. One possible weakness is that US military are not directly involved in the bombing of Yemen, as they were in Yugoslavia; but there might be sufficient action flying military support to constitute “hostilities,” a broader word intentionally chosen in the Vietnam era to avoid quibbles over defining “war.”

The Judicial Branch will thus have the opportunity to resolve one of the longest pending and most critical disputes between the Congress and the President: whether Congressional approval is needed before a President can involve our country in hostilities overseas. No one disputes the President’s inherent authority to act immediately in response to an attack, like Pearl Harbor. Yemen, and Yugoslavia before it, however, did not present that situation. There was time to bring the matter to the US Congress for its deliberation. It is shameful that federal courts have used every dodge they could to avoid deciding this important question, from the Korean War to the Vietnam War to today. Our long wait may soon be over.

Tom Campbell is the Dee and Doy Henley Distinguished Professor of Jurisprudence at Chapman University’s Fowler School of Law. He is also a Professor of Economics at Chapman. He is the author of Separation of Powers in Practice, published by Stanford University Press. He served five terms in Congress, including on the International Relations and Judiciary Committees.